What is sodium?
Sodium is an essential nutrient required for regulating blood volume and blood pressure in the human body.
AdvertisementsSodium deficiency disease, medically termed as 'hyponatremia' results when the serum sodium (Na+) drops below optimum level of 135 mmol/L (mEq/L). It is a serious electrolyte imbalance with devastating effects on the cerebral function, if neglected. Serum Na+ levels suddenly dropping below 115 mEq/L is a very serious state of health and medical emergency.
Sodium deficiency diseases have multifactorial etiologies and may present multiple causes in the same patient. In some diseases, such as heart failure, hepatic cirrhosis, severe diarrhea, persistent vomiting, excessive thirst or renal salt-wasting, both sodium and water homeostasis go awry. This sodium or/and water imbalance may evolve into an emergency. The treatment may be required to be started before a confirmatory diagnosis. Both over-correction and under-treatment have the risk of leading to central pontine myelinolysis, manifesting as paralysis.
Sodium food sourcesThe principal source of sodium in the diet is table salt (sodium chloride). Pickled and processed foods are good sources of sodium. It is also present in baking soda, monosodium glutamate (MSG), various seasonings, meat products, fish, poultry and dairy products. Plants and plant sources are generally poor sources of this nutrient. The minimum physiological requirement of sodium (Na) is 500 mg/day. The Adequate Intake for Na is 1.2 to 1.5 grams/day. The tolerable upper intake (UL) level for Na is 2.3 grams/day. Exceeding the UL could lead to hypertension and cardiac disease.
Sodium absorption and excretionThe absorption of sodium and water in the upper intestine depends on the presence of D-glucose. The active NA+ and glucose transport is by the Na+/glucose cotransporter (SGLT1). There is cotransport of water along with Na+ and sugar across the brush border membrane of enterocytes. The 3Na+/2K+ pumps on the basolateral membrane pump out Na+ towards the blood. The bulk of the sodium excreted is reabsorbed in the proximal tubule and ascending loop of Henle. A small quantity of sodium is delivered into the collecting duct for excretion in urine to maintain sodium balance.
Functions of sodiumSodium is required for controlling blood pressure and blood volume. Another important function of Na+ is maintaining cellular osmotic processes. Na+ is required for transmitting nerve impulses and normal function of the nervous system. Optimum Na+ serum level is required for contraction of muscles.
Sodium deficiency disease causesThe primary causes of low Na+ serum levels are, loss of sodium from the body, loss of sodium and water from the body or increase in the volume of water in the system. Low Na+ serum levels are common in elderly. Several factors contribute to excess water or fluid in the body or depletion of Na+. Some of the causative factors are:
- acute dietary deficiency,
- excessive sweating,
- drinking too much water,
- persistent vomiting,
- severe diarrhoea,
- fluid loss due to burns,
- kidney failure,
- congestive heart failure,
- hepatic cirrhosis,
- adrenal insufficiency,
- SIADH (syndrome of inappropriate anti-diuretic hormone),
- inappropriate vasopressin secretion,
- use of certain diuretics, antidepressants and anti-seizure medications,
- use of psychoactive medicines like MDMA,
- salt-wasting nephropathy,
- cerebral salt wasting,
- presence of tumors,
- use of antineoplastic agents and
- congenital chloride diarrhea.
Sodium deficiency signs and symptomsWhen hyponatremia is sudden, acute and severe, cerebral edema occurs leading to brain damage. In chronic form of the disease, the following symptoms may be observed:
- Weakness and tiredness,
- muscle weakness,
- loss of appetite,
- nausea and vomiting,
- increased falls,
- gait abnormality,
- altered posture and gait,
- spasms or cramps,
- reduced attention,
- altered personality,
- memory loss,
- fluid in the lungs,
- respiratory arrest,
- decreased consciousness and
Diagnosis of sodium deficiencyThe symptoms of low Na+ serum levels varies among patients. Measuring the serum levels of Na+ is the best way of confirming the diagnosis. Medical history of the patient will help in arriving at the causative factor. Determining the type of hyponatremia (i.e. hypervolemic, euvolemic or hypovolemic) can help in taking treatment decisions.
Sodium deficiency diseasesAs said earlier, the medical term for low Na+ serum levels is hyponatremia. Consumption of high volumes of fluid and excess loss of sodium are main precipitating factors. These fluid and sodium imbalances can be brought about by several factors listed above. Several systemic diseases can cause sodium deficiency in the serum.
HyponatremiaHyponatremia can set in suddenly and turn severe. In such acute state, water enters the brain cells causing cerebral edema. Herniation of the brain, brain stem compression and brain damage may occur. The acute deficiency state can also lead to fluid accumulation in the lungs and respiratory arrest. When the sodium serum level drop is gradual, the symptoms develop slowly over several days. Depending upon the causative factors, the type of hyponatremia (i.e. hypervolemic, euvolemic or hypovolemic) as well as the symptoms may vary.
Hyponatremia and tumorsAdedayo A. Onitilo et al. in their study "Tumor-Related Hyponatremia" concluded that,
- "Hyponatremia occurs quite frequently in patients with tumors. The systemic manifestation of many types of tumors and the toxicities of cancer therapy are involved in the pathogenesis of hyponatremia of malignancies."
Hyponatremia and congenital chloride diarrheaCongenital chloride diarrhea is due to mutations in the SLC26A3 gene resulting in intestinal SLC26A3 protein deficiency and impaired intestinal Cl(-)/HCO(3)(-) exchange. The mutation results in diarrhea-related sodium chloride and fluid depletion.
Sodium deficiency disease treatmentMild drop in serum Na+ levels is treated by oral hydration and electrolyte replacement. In severe or acute cases, treatment often involves intravenous fluid and electrolytes restoration. The patient's blood volume status, also has to considered for selecting the treatment option. Further medications may be required to treat and manage the factors responsible for the sodium deficiency disease.
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